Flash Tip: Understanding the "Lock Fill" Option with Gradients
From Adrien-Luc Sanders, former About.com Guide
Many people don't ever notice the "Lock Fill" button, or even understand what it does until they run afoul of it one day while wondering why their gradients aren't working properly. The Lock Fill button can be found under the options area of the Fill tool, and only works on gradients. This setting controls whether a gradient fill will span only one shape, or will span all shapes filled by that gradient. See the next steps for examples.